[desktop] Change ID from .desktop to .qt

required to publish on Flathub, and .desktop is a file extension anyway so it's a bad idea
also some improvements to metadata structure, and add branding colours
and fix the welcome message in qt

Signed-off-by: Harry Bond <me@hbond.xyz>

packaging/app.comaps.qt.metainfo.xml

@@ -1,15 +1,18 @@
 <?xml version="1.0" encoding="UTF-8"?>
+<!-- Copyright 2025 The CoMaps Community -->
 <component type="desktop-application">
-  <id>app.comaps.desktop</id>
+  <id>app.comaps.qt</id>
+  <metadata_license>CC0-1.0</metadata_license>
+  <project_license>Apache-2.0</project_license>
+  <content_rating type="oars-1.1" />
 
   <name>CoMaps</name>
+  <summary>Free offline maps for everyone</summary>
   <developer id="app.comaps">
     <name>The CoMaps Community</name>
   </developer>
-  <summary>Free offline maps for everyone</summary>
 
-  <metadata_license>CC0-1.0</metadata_license>
-  <project_license>Apache-2.0</project_license>
+  <launchable type="desktop-id">app.comaps.qt.desktop</launchable>
 
   <supports>
     <control>pointing</control>
@@ -17,15 +20,12 @@
     <control>touch</control>
   </supports>
 
-  <content_rating type="oars-1.1" />
-
   <description>
     <p>
       CoMaps is a free Android &amp; iOS offline maps app for travellers,
       tourists, hikers, drivers and cyclists.
       It uses crowd-sourced OpenStreetMap data.
     </p>
-    <p>## Features</p>
     <p>
       The Linux version of CoMaps does not have feature parity
       with the Android and iPhone versions, and has not yet been
@@ -33,6 +33,11 @@
     </p>
   </description>
 
+  <branding>
+    <color type="primary" scheme_preference="light">#456644</color>
+    <color type="primary" scheme_preference="dark">#375237</color>
+  </branding>
+
   <url type="homepage">https://comaps.app</url>
   <url type="bugtracker">https://codeberg.org/comaps/comaps/issues</url>
   <url type="faq">https://www.comaps.app/support/</url>
@@ -43,7 +48,6 @@
   <url type="vcs-browser">https://codeberg.org/comaps/comaps</url>
   <url type="contribute">https://codeberg.org/comaps/comaps/src/branch/main/docs/CONTRIBUTING.md</url>
 
-  <launchable type="desktop-id">app.comaps.desktop.desktop</launchable>
   <screenshots>
     <screenshot type="default" environment="plasma">
       <image>https://www.comaps.app/images/screenshots/Desktop_light_routing.png</image>
@@ -64,7 +68,7 @@
   </screenshots>
 
   <releases>
-   <release version="2025.07.13-9" date="2025-08-07">
+   <release version="2025.07.13-9" date="2025-08-09">
      <description>
        <p>CoMaps is now on Linux!</p>
      </description>